all the cool kids are doing it

A couple of times we’ve had machines that were newly encrypted with FileVault 2 give us the “circle-with-slash” on boot. Booting to verbose mode mentioned some PGP information, which shouldn’t be there. If that happens, boot to the recovery Partition and decrypt via Disk Utility or perform a CoreStorage revert via Terminal. Once you can access the partition again, look for /System/Library/Extensions/PGPwde.kext and /Library/PriviledgedHelperTools/com.pgp.framework.PGPwde and remove them if present. Try FileVault again and you’ll probably have better luck.